O. Zargari: It should be kept
in mind that hemosiderotic variant of dermatofibroma may be confused
with pigmented lesions including blue nevus. Interestingly
this issue has been addressed in a recently published paper;

Dermatofibroma is a common fibrohistiocytic tumor, it occur as
papules or nodules on the extremities in approximately 80%
of cases.

The
legs of women are a common location, possibly as a
result of shaving or other minor trauma, and there
are reports of cases involving the palms and soles. Although
they have been reported to occur at any age, dermatofibromas
most frequantly affect individuals in early to middle
adult life (as in this case).

There is no racial predilection. Although usually solitary, in
about 20% of patients multiple lesions will be found, and there
are reports of generalized dermatofibromas, especially in
immunosuppressed patients.

Dermatofibroma begins as a dusky red macule that quickly becomes
a papule composed mostly of granulation tissue in company with
innumerable extravasated erythrocytes within the dermis. Soon
macrophages appear in abundance, and by ingestion of components
of blood acquire the attributes of siderophages and lipophages.
The lesion may become nodular and even tumorous, and
progressively more firm as a consequence of production of
altered collagen by proliferating fibrocytes. In time,
fibroplasia predominates over granulomatous inflammation, and as
more melanin is formed within the epidermis, the hard,
dome-shaped lesion becomes browner. In time, after many years,
the lesion slowly flattens consequent to shrinkage by
fibroplasia. Sometimes the shrinkage is so great that the lesion
at last is a hyperpigmented dell (as in this
case).

Differential diagnosis

Includes scar, keloids, xanthomas, neurofibromas, kaposi’s
sarcoma, atypical nevus, and melanoma. A simple maneuver to help
confirm the diagnosis can be done by applying lateral
compression, which causes the central portion of the
dermatofibroma to “dimple”. Larger lesions that extends into the
fat and are several centimeters in diameter may be confused with
dermatofibrosarcoma protuberans.

Histopathology

Dermatofibromas are usually well circumscribed nodules confined
to the dermis, measuring 1-2 cm in diameter and composed of
plump fibroblasts arranged as intersecting fasicles. The likely
cell of origin is the dermal dendrocyte. There are variable
proportions of mononucleated and multinucleated foamy
histiocytes, with hemosiderin deposits in their cytoplasm.
Scattered between the cells, and predominantly at the periphery
of the lesion, are thick “keloidal” collagen bundles that are
birefringent when examined with polarizing lenses. Additional
features are epidermal hyperplasia and a perivascular
lymphoplasmacytic infilterate at the periphery of the nodule.

Treatment

None,
unless a lesion grows to several centimeters in diameter, when
simple surgical excision may be indicated.